I have done upgrades to SA1000, 2000, 3000, and limited stuff on the 5000 which is very hard to work on.
The SA5.1 schematic is floating around the Internet and the official one available from Catherine Weber per Altavista. Both Bigkidz and I have similar ideas of what Mike used to do with the mods (chokes, resistors, oil bypass, naked vishays, Non inductive WW plate resistors, etc.) It wont be 100% what the premium / gold level mods Mike used to offer but the ideas would be close.
Bringing a box to spec by replacing noisy resistors and old lytics is easy. Executing the mods take a lot of creative mounting work due to the 1U size of the SA5.1 vs the the HUGE size of the oil caps and the modern better sounding coupling caps (there is a reason why Mike sticks with Dynamicaps)
-Johnson